Balloon catheters are commonly used to treat certain conditions of a blood vessel, such as a partial or total occlusion or lesion of the vessel that may be caused by, for example, atherosclerotic plaque or thrombosis. In an angioplasty procedure, a guidewire is inserted into an occluded blood vessel. A balloon portion of a catheter is advanced over the guidewire to the site of the occlusion. When the balloon portion is properly positioned relative to the occlusion, the balloon portion is inflated. The inflating of the balloon portion of the catheter compresses the occlusion and thereby, restores normal blood flow through the blood vessel.
In some instances, a stent may be implanted in the blood vessel to help prevent the occlusion from recurring. It is common for a stent to be delivered to the site of an occlusion and deployed using a balloon catheter. In such a case, the stent, in an unexpanded condition, is mounted on the uninflated balloon portion of the catheter. When the stent is properly positioned relative to the occlusion, the balloon portion of the catheter is inflated. The inflating of the balloon portion of the catheter expands the stent in the blood vessel.
Difficulties often arise when treating an occlusion that occurs at or near a vascular bifurcation formed by an intersection of a main vessel with a branch vessel. A common method for treating such an occlusion involves implanting a first stent in the main vessel adjacent to the bifurcation. After the first stent is implanted in the main vessel, a second stent is implanted in the branch vessel at a location adjacent to the bifurcation. This procedure is often difficult and time consuming. One common difficulty that is encountered during this procedure involves threading a guidewire for the balloon catheter used to deliver the second stent through the struts of the implanted first stent. Another common difficulty arises when the implantation of the first stent causes plaque to close the branch vessel at the location of the bifurcation. When the branch vessel becomes closed, insertion of the guidewire into the branch vessel is extremely difficult.
Prior to placement of one or more stents in a blood vessel, it is common for the occlusion to be pre-dilated using a balloon angioplasty procedure. In preparation for a balloon angioplasty procedure at a vascular bifurcation, a first guidewire is inserted into the main vessel and a second guidewire is inserted into the branch vessel. FIG. 7 illustrates a vascular bifurcation 110 in which first and second guidewires 112 and 114, respectively, are located. As FIG. 7 illustrates, the first guidewire 112 extends through the main vessel 116 past the junction of the branch vessel 118. The second guidewire 114 extends through the main vessel 116 to the branch vessel 118 and then extends into the branch vessel. FIG. 7 also illustrates an occlusion 120 (a deposit of plaque) at the bifurcation. It should be noted that the occlusion 120, which may be caused by a stenosis or restenosis in the blood vessel, may be located in the main vessel upstream of the branch vessel, in the main vessel downstream of the branch vessel, at the intersection of the main vessel and the branch vessel, in the branch vessel downstream of the main vessel, or in a combination of any of these locations.
When the first and second guidewires 112 and 114 are inserted prior to the balloon angioplasty procedure, the second guidewire enables access to the branch vessel even if shifting plaque closes off the branch vessel during the balloon angioplasty procedure. In most known stenting procedures for treating occlusions at vascular bifurcations, however, the second guidewire must be withdrawn from the branch vessel prior to a stent being implanted in the main vessel so that the second guidewire will not interfere with the deployment of the stent in the main vessel. Consequently, difficulty may be experienced in re-inserting the second guidewire into the branch vessel.
FIG. 8 illustrates a segmented balloon catheter 130 disclosed in U.S. Pat. No. 6,761,734. The segmented balloon catheter 130 of FIG. 8 includes a single shaft 132 upon which first and second balloon portions 134 and 136, respectively, are mounted. A longitudinal passageway 138 extends through the shaft 132. A transverse port 142 extends through the shaft 132 at a location between the first and second balloon portions 134 and 136. The segmented balloon catheter 130 of FIG. 8 enables a first guide wire 146, which is pre-positioned in a main vessel 148, to be inserted into the shaft 132 and threaded through the longitudinal passageway 138 and out of an opposite end of the shaft. The segmented balloon catheter 130 also enables a second guide wire 152, which is pre-positioned in a branch vessel 154, to be inserted into the transverse port 142 and threaded through the longitudinal passageway 138 and out of an end of the shaft 132. The segmented balloon catheter 130 is useful for delivering and implanting a stent 158 in the main vessel 148.
One problem arising from the use of the segmented balloon catheter 130 of FIG. 8 results from the shape of the first and second balloon portions 134 and 136 adjacent the transverse port 142. As FIG. 8 illustrates, adjacent ends of the first and second balloon portions 134 and 136 are generally frustoconical and taper away from one another. As a result, a gap 160 located between the first and second balloon portions 134 and 136 is quite large relative to an axial length of the segmented balloon catheter 130. For example, a twenty millimeter long segmented balloon catheter 130 may have up to five millimeters between the first and second balloon portions 134 and 136 at the gap 160. This large gap 160 at the center of the segmented balloon catheter 130 may result in a non-uniform stent deployment. Specifically, the central portion of stent 158 may not be expanded to the same diameter as the proximal and distal ends of the stent, as FIG. 8 illustrates.